Magnetic materials are key components in a large number of technologies and devices such as car starters and alternators, microwave bandpass filters, and insertion devices for synchrotron radiation sources. Permanent magnets are an important class of magnetic materials and are defined as materials that retain a high degree of magnetization after a magnetizing field is removed. The amount of magnetic energy stored per the material's unit volume has increased ten-fold in the past few years due to technological progress in the synthesis of modern permanent magnets which feature rare-earth atomic constituents. This has allowed miniaturization of permanent magnets and increased versatility in their use. The resulting complex artificial structures, however, feature not only more than one type of magnetic atom, but atoms of the same species in different atomic environments. The simultaneous presence of rare-earth constituents in dissimilar crystal sites, or atomic environments, hinders our ability to understand their individual magnetic contributions by means of current detection methods. Not being able to fully understand existing materials inhibits the ability to develop new generations of permanent magnetic materials with improved performance in areas such as magnetic hardness (stability against demagnetizing fields) which are dictated by the interaction of magnetic moments with the local crystalline environment. Previous attempts to understand these properties have used established techniques such as Mossbauer spectroscopy and neutron diffraction. More recently, x-ray magnetic circular dichroism has also been used to detect and measure these and other characteristics of magnetic materials.
The main limitation of the neutron diffraction technique is that it probes all magnetic elements simultaneously. In the case of modern high-strength magnets, the majority of the magnetic atoms in the structure are transition metal atoms, such as Iron, while only a minority are rare-earth type. The magnetic hardness, however, is dominated by the minority rare-earth atoms. Understanding and improving magnetic hardness requires accurate detection of magnetic signals from these rare-earth atoms only. This is not possible using neutron diffraction. Finally, x-ray magnetic circular dichroism can separate magnetic contributions by element type, but cannot separate contributions from the same element in nonequivalent crystal sites or atomic environments. Only in special circumstances, where absorption thresholds between atoms in nonequivalent sites are large enough (vary rare), can this technique yield the information needed. In summary, none of the methods briefly discussed above, even when taken together, have been able to provide a complete understanding of the way in which modern permanent magnetic materials function and behave.